Bilge pumps in boats or ships must be activated before accumulating water reaches an excessive level. Early bilge pumps were activated manually or by mechanical switches such as those that have floats with contacts to complete electrical circuits and activate the bilge pumps. These mechanical switches typically performed as desired when initially installed on the boats. However, bilge debris and other contamination built up over time and/or caused corrosion to prevent the mechanical components from moving as intended. Additionally, these mechanical switches had relatively short lives compared to the boats in which they were installed and required replacement.
In an attempt to solve these problems with mechanical switches, electronic switches without moving parts were developed. Typically, these electronic switches utilize the conductivity of the water to be sensed with probes to activate the bilge pumps. These electronic switches are susceptible to false alarms, which can b “burn up” the pump motor, and missed detections, which can sink or damage the boat, once contamination in builds up around the probes, sloshing bilge water contacts the switch, and/or there are changing environmental conditions around the switch.
Many attempts have been made to solve these problems with electrical capacitive switches. Coated water repellant probes have been used. For example, see U.S. Pat. No. 4,276,454, the disclosure of which is expressly incorporated herein in its entirety by reference. Ultrasonic field detection has been utilized. For example, see U.S. Pat. No. 4,881,873, the disclosure of which is expressly incorporated herein in its entirety by reference. Acoustic transducers have been utilized. For example, see U.S. Pat. No. 4,897,822 , the disclosure of which is expressly incorporated herein in its entirety by reference. Time delays have been utilized. For example, see U.S. Pat. No. 5,404,048 , the disclosure of which is expressly incorporated herein in its entirety by reference. Optical fibers have been utilized. For example, see U.S. Pat. No. 5,425,624 , the disclosure of which is expressly incorporated herein in its entirety by reference. Field effect “touch sensors” have been utilized. For example, see U.S. Pat. No. 7,373,817 , the disclosure of which is expressly incorporated herein in its entirety by reference. While these attempts may have been somewhat successful in reducing false alarms and missed detections, they are either not completely successful or relatively expensive solutions. Accordingly, there is a need for improved bilge pump switches that are less costly and reduce false alarms and missed detections.